Nitrate (NO 3 − ) is a major nutrient for plants, taken up by their roots from the soil. Plants are able to sense NO 3 − in their environment, allowing them to quickly respond to the dramatic fluctuations of its availability. Significant advances have been made during the recent period concerning the molecular mechanisms of NO 3 − sensing and signaling in the model plant Arabidopsis thaliana. The striking action of NO 3 − as a signal regulating genome expression has been unraveled. Note worthily, NO 3 − sensing systems have been identified. These correspond to membrane transporters also ensuring the uptake of NO 3 − into root cells, thus generalizing the nutrient ‘transceptor’ (transporter/receptor) concept defined in yeast. Furthermore, components of the downstream transduction cascades, such as transcription factors or kinases, have also been isolated. A breakthrough arising from this improved knowledge is a better understanding of the integration of NO 3 − and hormone signaling pathways, that explains the extraordinary developmental plasticity of plants in response to NO 3 − .